Metal roof structures typically comprise a series of parallel rafter beams extending across the building in one direction and purlin beams parallel to each other mounted on top of the rafters extending in a direction normal to the rafters. The purlins are often joined together by support bracing or straps for extra support. Insulation material in long sheets is placed in the area between purlins. The sheets of insulation material can be laid along the length of the purlins or across the purlins in a direction normal to the purlins. Hard roofing material such as metal decking is then attached on top of the purlins over the insulation material. Because the hard roofing material comes in long sheets and the roofs generally have two sloped sections, it is customary to construct the roof along the width of the sloped section and then proceed along the length of the structure from one end to the other. The workers stand on the previously laid section of roof to construct the next section.
The insulation material must be supported between the purlins, and various methods of support have been used. Mounting straps or wire mesh that are attached to the purlins by forming a lattice have been used. This is referred to as banding. A sheet, typically made of vinyl and acting as a vapor barrier, is then rolled onto the lattice, and insulation material is placed between adjacent purlins and over the sheet. If the installation of the lattice is done from underneath the roof structure, scaffolding or lifting equipment is required.
Some systems dispense with the lattice and use the sheet itself to support the insulation material. The support sheet is draped from the adjacent purlins and the insulation material is placed on top of the support sheet. A carriage is used to aid in the dispensing of the support sheet. The carriage is positioned on top of the purlins and travels the length of the purlins during the roof construction. A roll of the support sheet material is mounted on the carriage and the support sheet is dispensed from the roll and placed on top of the purlins. As the carriage travels the length of the purlins the support sheet is draped across the purlins.
The carriage has guides that guide the carriage along the length of the purlins to insure that the carriage tracks correctly along the purlins. The guides also insure that the carriage does not move laterally with respect to the purlins. The guides prevent the carriage from falling between the purlins and insures that the support sheet is properly dispensed between the purlins. The guides have a downwardly extending member that is mounted on the carriage and near the side of a purlin. If the carriage were to move in a lateral direction the guide would contact the purlin and prevent any further lateral movement in that direction. For example, guides having an L-shaped cross-section have also been used to guide the carriage. The L-shaped guides have a laterally extending leg that slides on the top surface of the purlins and a downwardly extending leg that contacts the side of the purlin. Two opposing guides are mounted on the carriage and above two adjacent purlins.
These guides are typically bolted or rigidly fixed to the carriage in some other manner, such as welded or riveted. Because the purlin support bracing is generally attached towards the top portion of the purlin, the guides often hit the support bracing, and this prevents the carriage from traveling along the purlins. Bolts or rivets that extend up above the tops of the purlins may also obstruct parts of a guide, such as the laterally extending leg of the L-shaped guide. In these cases the carriage must be lifted up over the obstruction so that the carriage can continue moving along the length of the purlins. Since the carriage is fairly heavy and bulky, the lifting can be dangerous to the workers standing on the uncompleted roof structure. The guides can be unbolted or unfastened and temporarily removed until the carriage has passed the obstruction, but this is also dangerous to the workers since the carriage is riding on the purlins only and the workers must lean over the edge of previously laid section of the roof to get to the guides.
It would be desirable to have a system for building a roof structure that provides for an insulation support system which is convenient and efficient to construct.